Re: [patch 21/21] slab defrag: Obsolete SLAB

Christoph Lameter
2008-05-14T21:54:15Z

On Wed, 14 May 2008, Matthew Wilcox wrote:

> > Oh. The last message I got was an enthusiatic report on the performance
> > gains you saw by pinning the process after we looked at slub statistics
> > that showed that the behavior of the tests was different from your
> > expectations. I got messages here that indicate that this was a scsi
> > testing program that you had under development. And yes we saw the remote
> > freeing degradations there.
>
> What I said was:
>
> : I've also been playing around with locking the scsi_ram_0 thread to
> : one CPU and it has a huge effect on the numbers.
>
> : So we can see that scsi_ram_0 is clearly wandering between the two
> : CPUs normally; it takes up a significant (3 seconds ~= 7-8%) of the
> : execution time, and that locking it to one CPU (which interrupts tend
> : to be) improves the number of ops per second ... even of the CPU which
> : is forced to take all the extra work of running it!

The last message that I got on March 31st said:

>>I have a version below which tries to start the tasks at a similar time
>by using pause() and then signalling to wake all the tasks up. I don't
>?know a better way to start threads simultaneously ... maybe MAP_SHARED a
>file and write to it in one task while spinning in the other tasks
>waiting for it to change value?

>I've also been playing around with locking the scsi_ram_0 thread to one
>CPU and it has a huge effect on the numbers.

This indicated to me that you were still developing a test here and
discovered some startling things.

> Note the complete lack of comparison between slub and slab here! As far
> as I know, slub still loses against slab by a few % -- but I haven't
> finished running a comparison with -rc2 yet.

Indeed remote frees are slightly slower in some situations. Dont really
dispute that. I am just not sure that the TPC test is really suffering
from that symptom. I thought for a long time that the tbench regression
was due to a similar effect too until I got down to it.

> I thought you'd already run this test and were asking for the results of
> this to be validated against a real TPC run.

AFAICT the last state was that you were tinkering around with a test.

> I'm rather annoyed by this. You demand a test-case to reproduce the
> problem and then when I come up with one, you ignore it!

Ignore it? That is pretty strange statement given that I helped you
analyze the behavior of your test and understand what was going on the
system.